596 research outputs found
Non-normality and non-monotonic dynamics in complex reaction networks
Complex chemical reaction networks, which underlie many industrial and
biological processes, often exhibit non-monotonic changes in chemical species
concentrations, typically described using nonlinear models. Such non-monotonic
dynamics are in principle possible even in linear models if the matrices
defining the models are non-normal, as characterized by a necessarily
non-orthogonal set of eigenvectors. However, the extent to which non-normality
is responsible for non-monotonic behavior remains an open question. Here, using
a master equation to model the reaction dynamics, we derive a general condition
for observing non-monotonic dynamics of individual species, establishing that
non-normality promotes non-monotonicity but is not a requirement for it. In
contrast, we show that non-normality is a requirement for non-monotonic
dynamics to be observed in the R\'enyi entropy. Using hydrogen combustion as an
example application, we demonstrate that non-monotonic dynamics under
experimental conditions are supported by a linear chain of connected
components, in contrast with the dominance of a single giant component observed
in typical random reaction networks. The exact linearity of the master equation
enables development of rigorous theory and simulations for dynamical networks
of unprecedented size (approaching dynamical variables, even for a
network of only 20 reactions and involving less than 100 atoms). Our
conclusions are expected to hold for other combustion processes, and the
general theory we develop is applicable to all chemical reaction networks,
including biological ones.Comment: Software implementing our methods is available as a Github repository
at https://github.com/znicolaou/ratematrix and an animated version of Fig. 1
is available at
https://northwestern.box.com/s/otn3m2cov9gi3enht3r8jh5kjo9qnv6
Cilia Have a Significant Role in Regulating Cell Size in Response to Fluid Flow Induced Shear Stress in a Flow Chamber
Cilia are hair-like protrusions on the apical surface of cells. Their function is to relay mechanical signals like shear stress from extracellular into intracellular environment and thereby maintain cellular homeostasis. Ciliary dysfunctions include polycystic kidney disease and new therapeutic interventions based on ciliary function are under investigation. The current study evaluates the use of a custom designed fluid flow chamber’s ability to study the role of cilia in regulating cell size in response to shear stress.
A fluid flow chamber that continually maintains laminar flow at different flow rates and temperature was designed. Endothelial wild type cells (ETWT) that have cilia and polycystic kidney disease cells (PKD) that lost their ciliary function are grown on different glass slides. Cells on each glass slide are then exposed to continuous flow of phosphate-buffered saline at 37oC in the flow chamber. The optimal flow rate and duration of flow were first determined by measuring the total protein concentration before and after exposing the cells. Cell radius and area before and after exposing them to flow are measured using the NIS Software available on the microscope.
The results from protein concentrations (n=12) indicate that cells are still attached at normal physiological flow rate 467 mL/min (2.8 µg/µL) and did not significantly differ from 60 mL/min (4.08 µg/µL) or 600 mL/min (2.73 µg/µL). The results for duration of fluid flow (n=22) show that 60 minutes (0.09 + 0.01 µg/µL) is optimal compared to 120 minutes (0.06 + 0.01 µg/µL) or 180 minutes (0.10 + 0.02 µg/µL). Under these optimal conditions, the average area of ETWT cells (n=300) measured from different slides before and after the flow is 4420.81+ 67.40 µm2 and 4678.17 + 87.15 µm2 (n=200) respectively. For PKD cells, the average area before and after the flow (n=300) is 5682.46 + 105.48 µm2 and 4173.74 + 263.97 µm2 (n=250).
These results are in agreement with the published literature on the ability of cilia to maintain cell size in ETWT cells in response to shear stress that is similar to normal blood flow. However, under similar conditions, PKD cells could not maintain their cell size as the mechano-chemical signaling pathway that communicates external signals to prepare appropriate intracellular response is disrupted. These results provide confirmation that the custom designed parallel plate fluid flow chamber is a reliable tool to investigate the specific targets in the mechano-chemical cell signaling pathways
Discovery of Radio Outbursts in the Active Nucleus of M81
The low-luminosity active galactic nucleus of M81 has been monitored at
centimeter wavelengths since early 1993 as a by-product of radio programs to
study the radio emission from Supernova 1993J. The extensive data sets reveal
that the nucleus experienced several radio outbursts during the monitoring
period. At 2 and 3.6 cm, the main outburst occurred roughly in the beginning of
1993 September and lasted for approximately three months; at longer
wavelengths, the maximum flux density decreases, and the onset of the burst is
delayed. These characteristics qualitatively resemble the standard model for
adiabatically expanding radio sources, although certain discrepancies between
the observations and the theoretical predictions suggest that the model is too
simplistic. In addition to the large-amplitude, prolonged variations, we also
detected milder changes in the flux density at 3.6 cm and possibly at 6 cm on
short (less than 1 day) timescales. We discuss a possible association between
the radio activity and an optical flare observed during the period that the
nucleus was monitored at radio wavelengths.Comment: To appear in The Astronomical Journal. Latex, 18 pages including
embedded figures and table
MSX, 2MASS, and the LMC: A Combined Near and Mid Infrared View
The Large Magellanic Cloud (LMC) has been observed by both the Midcourse
Space Experiment (MSX) in the mid-infrared and the Two Micron All Sky Survey
(2MASS) in the near-infrared. We have performed a cross-correlation of the 1806
MSX catalog sources and nearly 1.4 million 2MASS catalogued point and extended
sources and find 1664 matches. Using the available color information, we
identify a number of stellar populations and nebulae, including main sequence
stars, giant stars, red supergiants, carbon- and oxygen-rich asymptotic giant
branch (AGB) stars, planetary nebulae, H II regions, and other dusty objects
likely associated with early-type stars. 731 of these sources have no previous
identification. We compile a listing of all objects, which includes photometry
and astrometry. The 8.3 micron MSX sensitivity is the limiting factor for
object detection: only the brighter red objects, specifically the red
supergiants, AGB stars, planetary nebulae and HII regions, are detected in the
LMC. The remaining objects are likely in the Galactic foreground. The spatial
distribution of the infrared LMC sources may contribute to understanding
stellar formation and evolution and the overall galactic evolution. We
demonstrate that a combined mid- and near-infrared photometric baseline
provides a powerful means of identifying new objects in the LMC for future
ground-based and space-based follow-up observations.Comment: 23 pages, 10 figures, to appear in the AJ (2001 Oct issue). N.B:
Tables 2 & 3 corrected and available as html file
Ursinus College Alumni Journal, November 1953
President\u27s page • A new year opens at Ursinus with 675 students • Approximately 100 students attend summer sessions • Ursinus welcomes two new members to its faculty • Ursinus evening school opens its second year • From the desk of the registrar • Alumni activities • News from the local alumni groups • Philadelphia square dance • Washington, D.C. hears President Glassmoyer • York alumni see baby pictures • 22 new M.D. graduates serving internship • Have you earned a Ph.D.? • Annual Cub and Key meeting on November 7 • Old timers\u27 day • Permanent class officers meet with loyalty fund committee • Ursinus bears beat Haverford 13 to 7 • Hockey field dedicated to Effie Brant Evans, \u2718 • A big thanks to class workers • Have you seen the new alumni office? • Memo from the executive committee • Sports review • Ray Gurzynski reviews the 1953 football prospects • Coach Harry Spangler sees bright prospect for his courtmen • Doc Baker reviews his 1953 soccer squad • Preview of 1953 wrestling • Hockey belles look forward to successful season • Pre-session camp at Ursinus fits phys-edders for 1953 sports • Ursinus is proud of its faculty • News about ourselves • Engagements • Weddings • Births • Christmas luncheon set for December 5, 1953 • Alumni basketball game January 19 • Necrologyhttps://digitalcommons.ursinus.edu/alumnijournal/1048/thumbnail.jp
An Early and Comprehensive Millimetre and Centimetre Wave and X-ray Study of SN 2011dh: a Non-Equipartition Blast Wave Expanding into a Massive Stellar Wind
Only a handful of supernovae (SNe) have been studied in multiwavelengths from the radio to X-rays, starting a few days after the explosion. The early detection and classification of the nearby Type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at one of the youngest phase ever of a core-collapse SN (days 3–12 after the explosion) in the radio, millimetre and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding SN shock wave does not exhibit equipartition (ϵe/ϵB ∼ 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R−2. Within modelling uncertainties we find an average velocity of the fast parts of the ejecta of 15 000 ± 1800 km s−1, contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast wave regime between the previously defined compact and extended SN Type IIb subtypes. Our results highlight the importance of early (∼1 d) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio ϵe/ϵB
- …